In recent years, optical imaging devices for simply and non-invasively measuring brain functions using light have been developed in order to observe the state of the brain's activity. In these optical imaging devices for measuring the brain functions, light sending probes placed on the surface of the head of a subject irradiate the brain with near-infrared rays having three different wavelengths: λ1, λ2 and λ3 (780 nm, 805 nm and 830 nm, for example), and at the same time, light receiving probes placed on the surface of the head detect the intensity of the near-infrared rays (information on the amount of received light) A(λ1), A(λ2) and A(λ3) of the respective wavelengths λ1, λ2 and λ3 emitted from the brain.
In order to find the product of the concentration of the oxyhemoglobin in the blood flow in the brain and the length of the optical path [oxyHb] and the product of the concentration of the deoxyhemoglobin and the length of the optical path [deoxyHb] from the thus-obtained information on the amounts of received light A(λ1), A(λ2) and A(λ3), simultaneous equations (1) to (3) are created using the modified Beer-Lambert Law, for example, and the simultaneous equations are solved (see Factors affecting the accuracy of near-infrared spectroscopy concentration calculations for focal changes in oxygenation parameters, NeuroImage 18, 865-879, 2003). Furthermore, the product of the concentration of the total amount of hemoglobin and length of the optical path ([oxyHb]+[deoxyHb]) is calculated from the product of the concentration of oxyhemoglobin and the length of the optical path [oxyHb] and the product of the concentration of deoxyhemoglobin and the length of the optical path [deoxyHb].A(λ1)=EO(λ1)×[oxyHb]+Ed(λ1)×[deoxyHb]  (1)A(λ2)=EO(λ2)×[oxyHb]+Ed(λ2)×[deoxyHb]  (2)A(λ3)=EO(λ3)×[oxyHb]+Ed(λ3)×[deoxyHb]  (3)Here, EO(λm) is the absorbance coefficient of oxyhemoglobin for light having a wavelength λm, and Ed(λm) is the absorbance coefficient of deoxyhemoglobin for light having a wavelength λm.
Here, the relationship between the distance (channel) between a light sending probe and a light receiving probe and the measurement portion is described. FIG. 12A is a cross-sectional diagram showing the relationship between a pair of a light sending probe and a light receiving probe and the measurement portion, and FIG. 12B is a plan diagram of FIG. 12A.
A light sending probe 12 is pressed against the surface of the head of a subject at a light sending point T, and at the same time, a light receiving probe 13 is pressed against the surface of the head of the subject at a Light receiving point R. Thus, the light sending probe 12 emits light, and at the same time, light emitted from the surface of the head enters into the light receiving probe 13. At this time, light emitted from the light sending point T on the surface of the head and that has passed through a banana-shaped region (measurement region) reaches the light receiving point R on the surface of the head. As a result, information on the amounts of received light A(λ1), A(λ2) and A(λ3) concerning the measurement portion S of the subject is gained particularly in the measurement region, where the measurement portion S is at the depth L/2 of which the length is half of the shortest distance connecting the light sending point T and the light receiving point R along the surface of the head of the subject from the middle point M of the shortest line L that connects the light sending point T and the light receiving point R along the surface of the head of the subject.
In addition, the optical imaging device for brain functions use a near-infrared spectrum analyzer, for example, in order to measure the product of the concentration of oxyhemoglobin and the length of the optical path [oxyHb], the product of the concentration of deoxyhemoglobin and the length of the optical path [deoxyHb], and the product of the concentration of the total amount of hemoglobin and the length of the optical path ([oxyHb]+[deoxyHb]), respectively, concerning a number of measurement portions in the brain (see Japanese Unexamined Patent Publication 2001-337033).
FIG. 13 is a block diagram schematically showing an example of the structure of a conventional near-infrared spectrum analyzer. In addition, FIG. 14 is a perspective diagram showing an example of the appearance of the near-infrared spectrum analyzer in FIG. 13. Here, for the purpose of simplicity, several optical fibers for sending light and several optical fibers for receiving light have been omitted.
A near-infrared spectrum analyzer 101 has a case 11 in rectangular parallelepiped form (70 cm×100 cm×120 cm, for example).
The inside of the case 11 is provided with: a light source driver (light emitting unit) 2 for emitting light; a light detector 3 for detecting light; an A/D 5; a control unit 21 for sending and receiving light; a control unit 22 for analysis; and a memory 23, and the outside of the case 11 is provided with: 16 light sending probes (light sending means) 12; 16 light receiving probes (light receiving means) 13; 16 optical fibers 14 for sending light; 16 optical fibers 15 for receiving light; a display device 26 having a monitor screen 26a; and a keyboard (input device) 27.
The light source driver 2 is a light source for sending light to the light sending probes 12, respectively, in response to a drive signal inputted from the control unit 21 for sending and receiving light and is made of semiconductor lasers LD1, LD2 and LD3 so as to emit near-infrared rays having three different wavelengths λ1, λ2 and λ3, for example.
The light detector 3 detects near-infrared rays received by the light receiving probes 13, respectively, so as to output 16 light receiving signals (information on the amounts of received light) A(λ1), A(λ2) and A(λ3) to the control unit 21 for sending and receiving light through the A/D 5 and is made of photoelectric multipliers, for example.
The optical fibers 14 for sending light and the optical fibers 15 for receiving light are tubes having a diameter of 2 mm and a length of 2 m to 10 m and can convey near-infrared rays in the direction of the axis in such a manner that the near-infrared rays that have entered from one end pass through the inside and are emitted from the other end or vice versa.
One optical fiber for sending light 14 is connected to one probe 12 for sending light and one semiconductor laser LD1, LD2 or LD3 in the light source driver 2 at the two ends so that they are away from each other by a set length (2 m to 10 m).
One optical fiber for receiving light 15 is connected to one probe 13 for receiving light a id one photoelectric multiplier in the light detector 3 at the two ends so that they are away from each other by a set length (2 in to 10 m).
This near-infrared spectrum analyzer 101 uses a holder 130 in order to make the 16 light sending probes 12 and the 16 light receiving probes 13 make contact with the surface of the head of a subject in a predetermined alignment. FIG. 15 is a plan diagram showing an example of the holder 130 into which the 16 light sending probes and the 16 light receiving probes are inserted.
Light sending probes 12T1 to 12T16 and light receiving probes 13R1 to 13R16 are aligned alternately in a matrix of four rows and eight columns. Thus, the distance between the light sending probes and the light receiving probes 13 is constant, and information on the amounts of received light A(λ1), A(λ2) and A(λ3) is obtained at a certain depth from the surface of the head. Here, the distance between the probes is referred to as the channel length, and in general, channels are 30 mm. In the case where the channels are 30 mm, information on the amounts of received light A(λ1, A(λ2) and A(λ3) is obtained at a depth of 15 mm to 20 mm from the middle point of the channels. That, is to say, points at a depth of 15 mm to 20 mm from the surface of the head approximately correspond to portions on the surface of the brain, and thus, information on the amounts of received light A(λ1), A(λ2) and A(λ3) concerning the brain's activity is obtained.
Different numbers (T1, T2 . . . , R1, R2 . . . ) are allocated to through holes in the holder 130 so that it can be recognized which light sending probe 12T1 to 12T16 or light receiving probe 13R1 to 13R16 has been inserted into which through hole, and at the same time, different numbers (T1, T2 . . . ) are allocated to light sending probes 12T1 to 12T16, respectively, and different numbers (R1, R2 . . . ) are allocated to light receiving probes 13R1 to 13R16, respectively. As a result, the light sending probes 12T1 to 12T16 and the light receiving probes 13R1 to 13R16 are inserted into the through holes of the corresponding numbers, respectively.
In addition, the curvature on the surface of the head of a subject differs depending on the difference in the sex, age and individual valuations, and therefore, the holder 130 can easily fit on the face of a head even if the curvature is different, where the support portions for holding the light sending probes 12T1 to 12T16 and the light receiving probes 13R1 to 13R16 are aligned in grid form on the surface of the head, and at the same time, the support portions are connected with each other through flexible connection portions, and moreover, the connection portions are rotatable within a predetermined angle with the support portions as a rotational axis (see Japanese Unexamined Patent Publication 2002-143169).
As for the positional relationship between the 16 light sending probes 12T1 to 12T16 and the 16 light receiving probes 13R1 to 13R16, it is necessary to adjust the timing in which the light sending probes 12 emit light and the timing in which the light receiving probes 13 receive light so that one light receiving probe 13 does not simultaneously receive light emitted from a number of light sending probes 12, but receives only light emitted from one light transmitting probe 12. Therefore, a memory 23 stores a control table that indicates the timing in which the light source driver 2 emits light and the timing in which the light detector 3 detects light.
This control table is stored in the memory 23 in the control unit 21 for sending and receiving light, which outputs a drive signal for sending light to one light sending probe 12 to the light source driver 2 at a predetermined time, and at the same time, the light detector 3 detects a light receiving signal (information on the amount of received light) received by a light receiving probe 13.
As a result, a total of 52 pieces of information on the amounts of received light (S1 to S52) A(λ1), A(λ2) and A(λ3) is collected, as shown in the plan diagram of FIG. 15.
In addition, a control unit 22 for analysis finds the product of the concentration of oxyhemoglobin and the length of the optical path [oxyHb], the product of the concentration of deoxyhemoglobin and the length of the optical path [deoxyHb], and the product of the concentration of the total amount of hemoglobin and the length of the optical path ([oxyHb]+[deoxyHb]) from the intensity of light having the respective wavelength (the wavelength absorbed by oxyhemoglobin and the wavelength absorbed by deoxyhemoglobin) that has passed through the optical path on the basis of the total of the 52 pieces of information on the amounts of received light A(λ1), A(λ2) and A(λ3) by using the simultaneous equations (1) to (3).
When a chronological change in the blood flow through portions in the brain of a subject while the subject is exercising, such as for rehabilitation, is attempted to be measured using the above-described near-infrared spectrum analyzer 101, a light sending probe 12T1 to 12T16 or a light receiving probe 13R1 to 13R16 may disengage from a through hole of the holder 130 because the case 11 with a size of 70 cm×100 cm×120 cm is fixed somewhere in a room. That is to say, the measurement procedure cannot be carried out when the movement of the subject is very active.
In addition, the time for a subject to exercise, such as for rehabilitation, is approximately one hour, and the time for a doctor to attach the holder 130 to the head of the subject and attach the light sending probes 12T1 to 12T16 and the light receiving probes 13R1 to 13R16 to the through holes of the holder 130 is also approximately one hour. That is to say, the preparation time during which the subject wears the holder 130 with the light sending probes 12T1 to 12T16 and the light receiving probes 13R1 to 13R16 on the head is very long as compared to the time during which the subject exercises, such as for rehabilitation.
Furthermore, the subject may exercise at home everyday, such as for rehabilitation, and it is almost impossible to provide the near-infrared spectrum analyzer 101 to every home, judging from the installment space and cost.
In addition, it is very troublesome for a family member to attach the holder 130 with the light sending probes 12T1 to 12R16 and the light receiving probes 13R1 to 13R16 to the head of the subject, and the subject alone cannot do this.